The present invention relates to a pitch control system for controlling the pitch of one or more blades. The pitch control system of the present invention is useful in any device that uses or converts the power of a moving fluid, or any device that transfers energy to, or generates movement in, a fluid. Such devices include windmills, wind motors, wind machines, wind turbines, water turbines and the like. More particularly, the present invention relates to a device for using the power of a moving fluid or generating movement in a fluid (such as a windmill, a wind motor, wind machine or wind turbine, water turbine, etc.) having radially placed blades capable of being rotated, and having a pitch control system for regulating the pitch of the blades, wherein the pitch control system comprises a pitch change shaft, means for translating the pitch change shaft in a horizontal direction, and coupling means between the pitch change shaft and the blades, said coupling means effecting a change in the pitch of the blades upon translation of the pitch change shaft.
The present invention furthermore relates to a hub for a windmill, wind motor, wind machine, wind turbine, etc. comprising a pitch control system.
A typical windmill, wind motor, wind machine or wind turbine comprising a pitch change element is known from European patent application EP-A-21810. Such a known device comprises a pitch change shaft extending in a hub of the device. The change shaft extends horizontally, and a toggle means are attached to the pitch change shaft. A change in position of the change shaft changes the position of the toggle means, which causes an arm, attached at one end to the toggle means and at the other end to an axis of a blade, to move, thereby, rotating the axis of the blade. The efficiency on the pitch system and of the device as a whole is dependent on a number of factors, among which the precision in pitch angle control is an important factor. Wear and tear are also important since they influence, among others the down time of a system (time needed for repairs and thus improductive) and the life time of a device. Wear and tear furthermore may after some time, result is a loss of precision in pitch control.
In the known system the toggle means exert transversal forces at right angles to the axis of the pitch change shaft directly on the pitch change shaft. Transversal forces on the pitch change shaft have the effect that rather than a movement of the pitch change shaft causing a change in the pitch of the system, in seeking the path of least resistance, a movement of the pitch change shaft causes a twisting of the pitch change shaft. Such a twisting causes wear and tear on the pitch change shaft. Such wear and tear ultimately necessitates repair of the pitch change shaft and thereby reduces the efficiency of the device. The transversal forces may even lead to the destruction of the pitch change shaft system. Equally or even more important is the effect that this twisting has on the precision in pitch angle control. A movement of the pitch change shaft results in a twisting of the pitch change system or partially in a twisting of the pitch change system and partially in a pitch change of the blades. The relation between the position of the pitch change shaft and the pitch angle of the blades thus becomes less precise (or even imprecise) and consequently the pitch angle control is less precise. A less precise pitch angle control reduces the efficiency of the device.
It is remarked that U.S. Pat. No. 4,534,705, patent abstracts of Japan, vol. 009, No. 034, and the abstract of JP 59 176472 each show devices having sliding means that slide over a central common shaft and to which pivoting means, coupled to the blades are provided. A change in position of the sliding means relative to the central shaft changes the pitch of the blades. The toggle means exert, via the sliding means transversal forces on the central shaft.
U.S. Pat. No. 4,257,736 discloses a wind mill which also does not comprise, for each blade, either a guide shaft and guide shaft sliding means, or first and second sub-coupling means. The blades are pivotably connected between a pair of parallel spaced plates such that the blade angle is adjusted in accordance with the relative spacing of the plates. This known device can basically only operate at two biasing arrangements and has very limited pitch control.
French Patent application FR 2355179 discloses a wind machine having a central axis to which side bars are connected, the side bars being movable in a direction along the central axis. Movement of the side bars changes the position of the blades.
Accordingly, it is desirable to provide a more efficient pitch control system having improved pitch angle control and reduced wear and tear on the pitch change shaft.
The mentioned and further objects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
The present invention provides pitch control systems, and devices using the same, having improved pitch angle control and reduced wear and tear on the pitch change shaft.
A device in accordance with the present invention includes coupling means comprising, for each blade, a guide shaft extending substantially parallel to each other and substantially parallel to the pitch change shaft. The coupling means further comprises first sub-coupling means coupling the pitch change shaft to the relevant guide shaft, said first sub-coupling means comprising guide shaft sliding means, and second sub-coupling means coupling the guide shaft sliding means to the relevant blade.
In a device in accordance with the present invention, the transversal forces exerted on the pitch change shaft perpendicular to the pitch change shaft axis are strongly reduced, due to the presence of the guide shafts extending substantially in parallel to the pitch change shaft. This enables better pitch control and reduces wear and tear. For a wind turbine this means better power control, for a wind machine this means stronger winds at the same power.
In one embodiment, the guide shafts are placed at substantially equal distances from the pitch change shaft, and arranged in a substantially symmetrical arrangement around the pitch change shaft. This provides for a symmetric pattern of reaction forces on the guide shaft, thus strongly reducing or even eliminating asymmetric loads on the central pitch change shaft.
The wear and tear on the guide shafts and any asymmetric forces the guide shafts exert on the pitch change shaft are also reduced and preferably minimised. To this end each guide shaft is preferably provided with adjustment means for adjusting the position and orientation of the said guide shaft. Such adjustment means enables the position of each guide shaft relative to the other guide shaft(s) and the pitch change shafts as well as their mutual parallelism to be controlled. The overall position of the guide shaft governs their mutual distances, whereas the orientation governs the (lack of) mutual parallelism. This allows for precision alignment of the guide shafts, which enables a further reduction or even elimination of internal hyperstatic reaction forces in the pitch system, enabling an improved pitch angle control and reduced wear and tear.
In one embodiment, the adjustment means comprises two or more adjustment sub-means separated from each other by some distance along the guide shaft. By using two or more adjustment sub-means separated some distance along the guide shaft the orientation (and thereby the mutual parallelism of the guide shafts) is more easily controllable.
In one embodiment, a first and a second adjustment sub-means are located at or near either end of each guide shaft. Such an arrangement provides for a large freedom in regulating/changing the orientations of the guide shafts, and furthermore the risk of interference with the sliding means is reduced. In one embodiment, each first and second adjustment sub-means includes 3 or more adjustment bolts in an adjustment sleeve. Using the adjustment bolts, the position and orientation of the guide shafts is easily and simply changeable.
In another embodiment, each first and second adjustment sub-means, includes six bolts regularly distributed over a circle, e.g., around the circumference of a guide shaft. Such an arrangement of bolts enables an easy and accurate positioning and orientation of the guide shafts.
In one embodiment each guide shaft, further includes a flat area for each adjustment bolt, the normal of each flat area being parallel to the longitudinal axis of the corresponding bolt. In this manner a bolt does not exert (or only to a very small amount) forces on the guide shaft other than directed along the longitudinal axis of the bolt (e.g., radially inward with respect to the guide shaft). Such an arrangement of opposing bolts helps prevent, or at least reduce torque from being exerted on the guide shaft.
In a further embodiment, each sliding means comprise two sliding sleeves, separated some distance from each other along the guide shaft, the inner diameter of said sliding sleeves exhibiting, initially, a difference.
Friction between the sliding means may be a cause of wear and tear as well as of generation of unwanted forces. Thus, in one embodiment, each sliding means comprises two guide sleeves, one initially having a slightly smaller inner diameter compared to the other guide sleeve. The sleeve having the smaller inner diameter will wear more than the other sleeve, until the diameters are substantially equal. The sliding means will then glide over the guide shaft guided by two sleeves of equal diameter, separated from each other along the guide shaft. Any sideways forces are in this arrangement distributed over two sleeves and over some distance along the guide shaft. This reduces the risk of concentration of harmful forces and thereby average wear and tear.
According to one aspect of the invention, an apparatus is provided having two or more radially placed blades capable of being rotated, and having a pitch system for regulating the pitch of the two or more blades. The pitch system typically comprises a pitch change shaft substantially extending in a horizontal direction, and coupling means coupling the pitch change shaft and the blades. The coupling means effects a change in the pitch of the blades upon translation of the pitch change shaft, wherein the coupling means typically comprises, for each blade, a guide shaft extending substantially parallel to each other and substantially parallel to the pitch change shaft, first sub-coupling means coupling the pitch change shaft to the relevant guide shaft, said first sub-coupling means comprising guide shaft sliding means, and second sub-coupling means coupling the guide shaft sliding means to the corresponding blade.
According to another aspect of the invention, a pitch control system is provided for controlling the pitch angle of two or more blades. The pitch control system typically comprises a pitch control shaft having a central translation axis, and a coupling system for coupling the pitch control shaft to the two or more blades. The coupling system typically comprises, for each blade, a guide shaft extending substantially parallel to the pitch control shaft, a guide shaft coupler, slidably coupled to the guide shaft, for coupling the guide shaft to the pitch control shaft, and a blade coupler for coupling the guide shaft coupler to the blade. The coupling system is arranged such that controlled movement of the pitch control shaft along the central translation axis causes a corresponding change in the pitch angle of the two or more blades.
Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.